The present invention relates to an indexable insert for turning which cutting insert has a polygonal basic form including an upper surface, and a bottom surface. The top and bottom surfaces are interconnected by side surfaces, wherein at least a part of the intersection lines between the side surfaces and the upper surface forms at least one main cutting edge, a secondary cutting edge and a curved corner cutting edge therebetween.
For copy turning nowadays, to a large extent, indexable inserts are used with nose point angles below 60xc2x0, wherein an ordinary value of the nose point angles is 55xc2x0, which enables application of the cutting inserts within a broad range. On the market nowadays a number of different types of indexable inserts with 55xc2x0 nose point angle are found, among which types rhomboidic, rhombic and regular triangular indexable inserts can be mentioned.
In copy turning the following properties regarding feature and economy are desirable:
1) Good chip control, i.e. favourable chip guidance and chip breaking.
2) No movement of the cutting insert under impact of cutting forces.
When copy turning inwards in certain materials or in slender work pieces and also in usage on unsteady machines and in internal metal working, low cutting forces and preferably a positive chip angle on the copying insert are also desirable. Simultaneously there is a demand in modern machines that the copy turning insert to be used will be able to give the best possible surface finish of the machined surface. Sometimes the surface finish can be improved by using higher cutting speed and neutral or positive rake angles.
It is a first purpose of the invention to achieve a new and improved indexable insert for copy turning having a new type of wiper edge in the corner region which enables attainment of improved surface finish of the machined surface.
It is a second purpose to achieve an insert with a rake face in the corner area that brings about a favourable influence on the cutting force and the tool wear.
It is a third purpose to achieve an insert that is modified such that it enables increased feed whilst maintaining good surface finish.
The present invention relates to an indexible cutting insert having a polygonal shape and including an upper surface, a lower surface, and an edge surface structure interconnecting the upper and lower surfaces. An intersection between the edge surface structure and the top surface forms: a main cutting edge, a secondary cutting edge, and a curved corner region disposed between the main and secondary cutting edges. The corner region includes a radial edge and a corner edge of mutually different radii of curvature. The radial edge and the secondary cutting edge are disposed on a first side of a bisector of the corner region, The corner edge and the main cutting edge are located on a second side of the bisector. A radius of curvature of the radial edge is at least five times larger than a radius of curvature of the curved edge. The top surface includes an edge-reinforcing land extending along the radial edge and the curved edge. A portion of the land extending along the radial edge being of smaller width than a portion of the land extending along the curved edge.